Templeton, A.S., Ellison, E.T., 2020. Formation and loss of metastable brucite: does Fe(II)-bearing brucite support microbial activity in serpentinizing ecosystems? Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, 20180423.

https://doi.org/10.1098/rsta.2018.0423 Ultramafic rocks undergo successive stages of hydration and oxidation during water/rock interaction, giving rise to secondary minerals such as brucite, serpentine, magnetite and the production of H . Ferroan brucite (Mg x 2(g) Fe 2+ (1-x) (OH) 2 ) (MgxFe(1-x)2+(OH)2) often forms under low water/rock ratios early during the 'serpentinization' process. The formation of ferroan brucite sequesters Fe(II) and suppresses the production of H , thereby limiting the flux of reductants suitable for sustaining microbial metabolism. Yet ferroan brucite is a 2 relatively soluble mineral 'reservoir' for reactive Fe(II). Brucite is often metastable and can be lost at later stages of peridotite hydration when there is a significant increase in the water/rock ratio or the activity of SiO 2 or CO . The Fe(OH) component of brucite has the thermodynamic potential to reduce most aqueous oxidants. 2 2 Therefore, ferroan brucite may reduce water and/or dissolved carbon, nitrogen and sulfur species, while the Fe(II) is converted into more stable secondary minerals such as Fe(II/III)-oxides and hydroxides (e.g. green- rust, magnetite, iowaite and pyroaurite) and ferric serpentine. The reactivity of ferroan brucite, and the associated rate of Fe solubilization and oxidation in subsurface fluids, could be a key regulator on the rate of electron transfer from serpentinites to the rock-hosted biosphere. Aqueous alteration of ferroan brucite may significantly modulate the H activity in fluids circulating within partially serpentinized rocks, and buffer H as 2 2 in situ it is lost by advection or consumption by a hydrogenotrophic microbial community. Moreover, there may be microbial organisms that specifically colonize and use ferroan brucite as an electron donor for their metabolism. The energy fluxes sustained by localized brucite oxidation may often be sufficiently large to sustain abundant microbial communities; water/rock reaction zones where brucite is consumed could serve as environments to search for extant or fossil serpentinite-hosted life.

Teng, J., Mastalerz, M., Liu, B., Gognat, T., Hauser, E., McLaughlin, P., 2020. Variations of organic matter transformation in response to hydrothermal fluids: Example from the Indiana part of the Illinois Basin. International Journal of Coal Geology 219, 103410.

http://www.sciencedirect.com/science/article/pii/S0166516219311619 Thermal maturation of organic matter in sedimentary rocks is a complex process controlled by multiple parameters. In this study, we examined the thermal history of one location in the Indiana part of the Illinois Basin. A total of 21 samples spanning the time interval from the Ordovician to the Mississippian were selected for maturity assessment and chemical structure characterization of vitrinite/vitrinite-like particles, solid bitumen, and alginite. The reflectance of vitrinite/vitrinite-like particles (VR ) reveals erratic variations with o depth from 0.61% to 1.18%. Solid bitumen reflectance (SBR ), ranging from 0.43 to 0.92%, is slightly lower o than VR across this maturity range in this borehole. In addition to documenting reflectance variations with o depth, variations within single organic matter particles were analyzed in the Upper Devonian New Albany Shale and Upper Ordovician Maquoketa Shale samples; these samples were targeted because they contained more organic matter than the samples from other stratigraphic units. SBR shows significant variations within a single o solid bitumen particle with a difference up to 0.81%. Significant maturity-related chemical differences within individual particles of solid bitumen and alginite were also revealed using micro-FTIR technique. An increase in temperature with depth of burial is certainly the key factor in controlling the thermal transformation of organic matter in sedimentary rocks. However, it is apparent that this mechanism alone does not explain the stratigraphic variations of VR throughout the core and reflectance variations within individual solid bitumen o and alginite particles. We suggest that the flow of hydrothermal fluids through the New Albany and Maquoketa Shale caused the observed thermal maturity anomaly. High concentrations of chlorine, vanadium, chromium, and zinc also suggest that organic matter transformation was enhanced by the flow of hydrothermal fluids in the study area.